Open heart surgery has been practiced for a number of years and the techniques for protection of the patient have been under study for all of this period. When the blood of the patient is by-passed to an extracorporeal support system which maintains the pumping function of the heart and the oxygenation function of the lungs, it is important that the heart itself be protected from ischemia, that is, deficiency of oxygenated blood in the heart muscles. In the circumstances of heart surgery, the possibility of damage to the heart is greatly reduced by cooling and administering drugs to the heart in a technique called "cardioplegia". A system for cooling the heart using the actual blood of the patient has also been developed and the use of blood as the vehicle for delivery of the cardioplegic solution has the advantage of keeping the heart oxygenated while it is arrested for the surgery.
Various methods for achieving cardioplegia have been used such as ice for slush baths with cooling coils submerged therein. Literature on the subject includes:
A Simple Method of Cold Coronary Perfusion, Hillel Lakes, M.D. et al, The Annals of Thoracic Surgery, Vol. 25, No. 4, April 1978 PA1 Cold Cardioplegia Versus Hypothermia for Myocardial Protection, The Journal of Thoracic and Cardiovascular Surgery, Vol. 76, No. 5, November 1978
The present invention relates to an improved system for achieving cardioplegia which can be used in conjunction with the life support equipment in a combined plan making it easier to control and administer the cold oxygenated blood and/or drugs. In previous techniques, the batch system has been used in which a quantity of the patient's blood is mixed with a quantity of medication in a single batch and then introduced into the patient's heart. From time to time, new batches might be requested by the attending surgeon and prepared and administered.
It is an object to provide a cardioplegic system which is more readily controlled and monitored and which enables the administration of the solution in a continuous fashion if desired as distinguished from the batch system. A roller pump can be used to control and monitor the cardioplegia flow rate, and temperature monitoring is available at a location convenient to an operator. In addition, the administration of drugs along with the cold solution has more reliability and reproducibility in this system and apparatus to be disclosed and the mixing of the medication and blood can be achieved in a much more efficient manner than can be done in the batch system.
In the present invention, an improved cooling coil, cooling bath and control is disclosed wherein the area of heat transfer is controlled by liquid level which is determined by a suitable flow valve adjustment.
An object of this system is to utilize a continuous flow of a coolant and to adjust fluid levels in the cooling system to vary the area of contact of the cooling coil and thus the temperature to be achieved.
A further improvement lies in a bubble trap to minimize the possibility of air entering the aorta, this being associated with a temperature monitor, and serving also in connection with a pressure isolator and pressure monitoring and limiting system.
The transparent bubble trap is placed at a highly visible location for an operator and in normal operation will function to remove such few bubbles as occur in a fully primed system. If there is a line break or a drug bag empties, there is the possibility of air entering the system. This will cause a change in the solution level in the bubble trap although the trap will continue to function as intended. A continued drop in level will warn the operator to shut down the system long enough to isolate the difficulty and remedy the flow pattern.
Other objects and features of the invention will be apparent in the following description and claims in which the principles of the invention are set forth together with a detailed disclosure of the manner and process of using the invention directed to persons skilled in this art to enable the practice of the invention, all in connection with the best mode presently contemplated for the invention.